Bicycles designed to traverse rugged terrain, commonly known as mountain bikes, have been available for many years. An increasingly common feature of mountain bikes is their rear suspension systems. The rear suspension system prevents certain forces from being transferred by the terrain, against the bike, to the rider. It also increases rider control by maximizing tire contact with the terrain.
Mountain bike rear suspension systems that use shock-absorbing elements have placed great emphasis on correcting the problem of “jacking.” See, for example, U.S. Pat. No. 5,899,480 to Leitner, which describes the “jacking” than can occur because of the design of “swingarm” rear suspension systems (“[i]n simple swingarm rear suspension [systems], the swing arms pivot sharply upward when a surge of power is supplied to the rear wheel, and pivot downward again when the power is backed off”). When a mountain bike is ridden over rough terrain, such “jacking” can reduce the contact of the rear wheel with the riding surface, which can severely compromise the rider's control over the bike. Additionally, in some prior art designs, forces are imparted to the seat tube (or any other area of the main frame that is not properly aligned with a key structural member of the frame), which creates forces on the bike that work against the forward propulsion induced by pedaling.
The rear suspensions of some prior art mountain bike designs can suffer from various deficiencies and inadequacies. For example, some frame designs require complicated manufacturing techniques to work around an uninterrupted seat tube and seat mast to mount a shock-activating link on the seat tube. This is due to the shape of the frame, which requires the seatpost to be constructed of two separate elements, thereby increasing the time needed to manufacture and assemble the components of the frame. This increases the cost of manufacturing and decreases the efficiency of workers and use of materials. Some frame designs utilize a link system that is not a structurally robust frame member, thereby creating a weak structural element. The rear shock in some frame designs is mounted to the frame by a means of an attached throughshaft, where one end of the shock rests and is bolted to the opposing side of the frame. This throughshaft can form a weak element of the frame. Other prior art mountain bike frame designs provide no or inadequate conduits or channels for the forces generated by the rider and the ground to be directed into strong load bearing structures.
What is needed is a mountain bike capable of efficiently channelling the external forces operating thereon, that does not jack or that exhibits a reduced tendency to jack, that is stronger, and that is lighter.